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1.
Models of the motion of the terrestrial reference frame with respect to an inertial frame can describe the motions of the Earth-Moon system, which are traditionally separated into precession, nutation, the polar motion, and rotation about the Earth’s axis. Existing theoretical models do not describe variations in the Earth-orientation parameters with the required accuracy, so that the current polar coordinates and duration of the day must be determined from observations. To improve theoretical models for the time dependence of the coordinates of the Earth’s pole, we examine the possible excitation of the Chandler wobble due to internal properties of the Earth-Moon system. A differential equation describing the parametric resonance in the Earth-Moon system is obtained for the first region of the parametric excitation. The solution of this equation analytically describes the finite amplitudes of the nonlinear conservative system. The theoretical results are compared with the empirical laws of Melchior deduced from observational data on the coordinates of the Earth’s pole. 相似文献
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Haiyang Yi Wenqing Wang Olaf Kolditz Hua Shao Hongwei Zhou 《Environmental Earth Sciences》2017,76(21):737
Numerical modelling of coupled physical processes in bentonite–sand mixtures under the geological conditions is significant for designing and constructing sealing systems in deep underground repositories for highly radioactive nuclear waste. Within the framework of DECOVALEX 2015, Task A, this work presents the model validation of OpenGeoSys by numerical modelling of coupled hydromechanical (HM) processes in bentonite–sand mixtures. Parameters used in the HM model were determined by modelling the laboratory tests of the sealing experiment (SEALEX). Afterwards these parameters were applied for the modelling of a small-scale mock-up test considering the influence of technological gap and incidental fail of the seal in the sealing system. In order to investigate the availability of employing these HM parameters and numerical models directly to field predictions, the modelling results and measured data of an in situ SEALEX experiment were analysed comparatively. The modelling results reproduced well the main features in HM behaviour of the compacted bentonite–sand mixture, which denotes that the adopted HM models and parameters are adequate for describing the HM processes in the sealing system. It is necessary to take the elastoplastic behaviour and evolution of the permeability of bentonite–sand mixtures into account when using the adopted models to reproduce the HM processes of a sealing system. 相似文献
4.
The integrity of wells, which are key components for CO2 sequestration, depends mainly on the seal between the wellbore cement and the geologic formation. To identify the reaction products that may alter the cement/caprock interface, batch experiments and computer modelling were conducted and analysed. Over time, the dissolution and precipitation of minerals alters the physical properties of the interface, including its tightness. One main objective of the simulation was thus to analyse the evolution of the porosity of cement and caprock over time. The alteration of the cement/caprock interface was identified as a complex problem and differentiated depending on rock type. The characteristic feature of a cement/shale contact zone is the occurrence of a highly carbonated, compacted layer within the shale, which in turn causes cement/shale detachment. In the case of a cement/anhydrite interface, the most important reaction is severe anhydrite dissolution. Secondary calcite precipitation takes place in deeper parts of the rock. The cement/rock contact zone is prone to rapid mineral dissolution, which contributes to increased porosity and may alter the well integrity. Comparison of computer simulations with autoclave experiments enabled the adjustment of unknown parameters. This enhances the knowledge of these particular assemblages. Overall, a good match was obtained between experiments and simulations, which enhances confidence in using models to predict longer-term evolution. 相似文献
5.
沉积盆地热体制研究的基本原理和进展 总被引：70，自引：2，他引：70
沉积盆地动态热体制研究可以分别在盆地和岩石圈两种尺度上进行，其目的是盆地热历史的重建或恢复。在盆地尺度下，热历史是通过地层中古温标（直接或间接的）反演而获得的；在岩石圈尺度下，则是通过盆地构造热演化模拟正演而获得的。古温标的动力学模型和盆地数学模型是正、反演过程的基础。本文综述了镜质体反射率、磷灰石裂变径迹和蒙脱石－伊利石转化三种主要古地温计的动力学模型和不同类型盆地成因模型的发展概况，勾画了盆地热历史重建正、反演方法程序的基本框架，并就几个相关问题提出了意见。最后介绍了新近开发出的油气盆地热历史及构造热演化模拟系统。 相似文献
6.
多层地基非轴对称Biot固结的理论解 总被引：1，自引：1，他引：0
提出了一种新方法来推导多层地基非轴对称Biot固结问题的传递矩阵,相应的理论推导工作量较少。基于柱坐标系下非轴对称Biot固结的基本方程,通过引入中间变量,并对坐标 进行Fourier级数展开,对时间 和坐标 进行Laplace-Hankel变换,得到了6×6阶和2×2阶的两组常微分方程;然后,两组常微分方程进行关于 的Laplace变换和逆变换,得到了单层地基非轴对称Biot固结问题的传递矩阵;结合边界条件和连续条件,运用传递矩阵法得到多层地基非轴对称Biot固结问题在Laplace-Hankel变换域内的解,通过Laplace-Hankel逆变换得到了该问题物理域的真实解答。编制了计算程序,并进行了数值计算与分析。该方法具有计算速度较快的特点,方便工程应用。 相似文献
7.
The behaviour of geodetic reference systems as a function of time cannot be ignored in determinations of position for secular geodynamic modelling. While non-specialist users are likely to appreciate the uncertainty surrounding the concept of a “fixed” point in regional surveys for crustal motion, its extension to global surveys based on techniques in dynamic geodesy is not widely understood. Such solutions are related to the natural coordinate system defined by the instantaneous geocentre (earth's centre of mass) and the instantaneous rotation axis whose location in earth space cannot be expected to be time invariant.The effect of such movements of the natural system of reference on the coordinates of points at the earth's surface is computed for a plausible model of the former. The resulting changes in solutions for three-dimensional position from dynamic considerations are discussed. It is shown that for the model adopted, the earth-space variations of the natural reference system with time produce coordinate changes with magnitudes not dissimilar to those resulting from reasonable variations in the earth's figure, though with different wavelengths, when computed from three-dimensional considerations alone.The resulting displacements, along with an accepted model for plate motions, are used to study changes in the shape of the level surfaces of the earth's gravity field with time. It is shown that plausible models for the deformation of the earth's figure produce significant changes in the geopotential and the shape of the geoid. However, the transfer of mass implied in extreme models of plate motion produce no significant changes in the datum level surface for crustal motion studies over periods as long as 102 yr. 相似文献
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There is wide interest in the results of studies of the dynamics of satellites of planets. Such data are needed to determine the physical properties of celestial bodies, and they may be able to provide information about the origins and evolution of the solar system. The general approach to studying the dynamics of satellites involves developing models for the motion and ephemerides based on observational data. Ephemerides are required to prepare and launch space missions to other planets and help discover new celestial bodies. High-precision astrometric coordinates of the principal satellites of Jupiter, Saturn, and Uranus are derived from photometric observations of occultations and eclipses of these satellites. To this end, worldwide observing campaigns have been organized. Enhancement in the precision of ephemerides can be obtained not only by increasing the accuracy of observations, but also by expanding the time interval covered by the observations. Many new, distant satellites of the major planets were discovered in the early 21st century. However, observations of these satellites are scarce and were obtained over short time intervals; as a result, some of these satellites were lost. To date, 179 natural satellites are known. This paper is based on a presentation made at the conference “Modern Astrometry 2017,” dedicated to the memory of K.V. Kuimov (Sternberg Astronomical Institute, Moscow State University, October 23–25, 2017).
相似文献9.
Problems with compositional data, like spurious correlation and negative bias, are well known in the Geosciences. Not so well known is the fact that the same problems appear when dealing with regionalized compositions. Here, these problems are illustrated, and a solution, based on the principle of working in coordinates using orthonormal logratio representations, is presented. This approach offers a tool for standard geostatistical studies. One of the advantages the method has is that it allows the usual inconsistencies with indicator kriging to be overcome through simplicial indicator kriging. A general way of modelling crossvariograms of coordinates, based on the matrix valued variation variogram, is discussed. In summary, the main aspects related to the modelling and analysis of regionalized compositions have had satisfactory solutions found for them. The proposed methodology is illustrated with public data from a survey concerning arsenic contamination in underground water in Bangladesh.
相似文献10.
《Physics and Chemistry of the Earth, Part A: Solid Earth and Geodesy》1999,24(2):131-137
Cellular Automata (CA), a paradigm of parallel computing, represent an alternative to differential equations and are used for modelling and simulating very complex phenomena; CA models have been developed by our research group for the simulation of landslides. We present SCIDDICA-3, our most efficient model, a two-dimensional CA model together with the simulation results of the Mount Ontake (Japan) debris avalanche which occurred in 1984. Landslides are viewed as a dynamic system based exclusively on local interactions with discrete time and space, where space is represented by square cells, whose specifications (states) describe physical and chemical characteristics (friction, viscosity, altitude, debris thickness, etc.) of the corresponding portion of space. At the time t=0, cells are in states which describe initial conditions; the CA evolves then changing the state of all cells simultaneously at discrete times. Input for each cell is given by the states in the adjacent cells; the outflow computation from the cells gives the evolution of the phenomenon. The comparison between the real and simulated event is satisfying within limits to forecast the surface covered by debris. 相似文献
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In this paper we consider crystallization of solid solutions and formation of growth zoning in minerals. To ascertain the role of various mechanisms producing zoning we have constructed kinetic models of nonsteady solid solution crystal growth. The equations obtained describe the temporal evolution of the solute and crystal composition. Since these equations are not solvable analytically we have solved them numerically by a fourth-order Runge–Kutta method. On the basis of this solution we can compute the zoning profiles for different crystallization modes and conditions. The constructed models have been used for study of mechanisms of zoning formation in metamorphic garnets. We conclude that the main mechanism of production of growth zoning is fractionation. The role of change of distribution coefficient in equilibrium crystallization is negligible. The modelling of zoning profiles reveals that simple arc-shaped profiles originate from crystallization in a closed system while complicated nonmonotonic profiles appear with crystallization in open systems under fluid flow. The duration of metamorphic garnet crystallization is estimated. 相似文献
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Caterina Gozzi Roberta Sauro Graziano Francesco Frondini Antonella Buccianti 《Environmental Earth Sciences》2018,77(16):579
Chemical reactions in aqueous geochemical systems are driven by nonequilibrium conditions, and their dynamics can be deduced through the distributional analysis (identification of probability laws) of complex compositional indices. In this perspective, compositional data analysis offers the possibility to investigate the behavior of the composition as a whole instead of isolated chemical species, with the awareness that multispecies systems are characterized by the simultaneous interactions among all their parts. We addressed this problem using D???1 isometric log-ratio coordinates describing the D compositional dataset of the river chemistry of the Alpine region (D number of variables), thus working in the \({{\mathbb{R}}^{D - 1}}\) statistical sample space. The D???1 coordinates were chosen using the decreasing variance criterion so that each one could provide information about different space–time properties for the investigated geochemical system. Coordinates dominated by heterogeneity appear to be able to capture regime shifts only on a long-time period and monitor processes on a very wide scale. On the other hand, coordinates characterized by lower variability present multimodality, thus capturing the presence of alternative states in the analyzed spatial domain also for the current time. Further developments are needed to determine the ranges of conditions for which variability and other statistics can be useful indicators of regime shifts on different time–space scales in geochemical systems. 相似文献
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The origin of snowball and sigmoidal inclusion patterns in porphyroblasts is discussed. Snowball garnets are peculiar to shear zones whereas sigmoidal patterns occur in porphyroblasts both in shear zones and on the limbs of folds. There are currently two models for the development of snowball garnets and these have been discussed extensively in the literature. We show that although the typical two-dimensional snowball pattern can be produced by either model, the three-dimensional inclusion patterns are model-specific thus providing a distinguishing criterion. We have applied this criterion to all the available data and find that the classical model, which is dependent on the rotation of garnet relative to a single foliation, is applicable in all cases. Syn-kinematic porphyroblasts on the limbs of horizontal normal folds generally show little rotation relative to geographical coordinates. What rotation they do show generally has the same sense as that of the host limb, but is less in magnitude. This has been used as evidence that the porphyroblasts have remained irrotational while the rocks deformed around them; the implication being that they were unaffected by vorticity associated with folding. This has been explained by claiming that the porphyroblasts are restricted in distribution to small domains of coaxial deformation path. We show that for reasonable deformation models of horizontal normal folds, porphyroblasts affected by vorticity will rotate little with respect to geographical coordinates and our results predict the commonly observed natural patterns. We conclude therefore that lack of rotation relative to geographical coordinates cannot be used to demonstrate that porphyroblasts have grown only in coaxially deforming domains; much less restrictive and more reasonable interpretations are possible. Consequently, the lack of rotation relative to geographical coordinates is more significant for fold modelling than it is for the garnet controversy. 相似文献
14.
David Savage Josep M. SolerKohei Yamaguchi Colin WalkerAkira Honda Manabu InagakiClaire Watson James WilsonSteven Benbow Irina GausJoerg Rueedi 《Applied Geochemistry》2011,26(7):1138-1152
The use of cement and concrete as fracture grouting or as tunnel seals in a geological disposal facility for radioactive wastes creates potential issues concerning chemical reactivity. From a long-term safety perspective, it is desirable to be able model these interactions and changes quantitatively. The ‘Long-term Cement Studies’ (LCS) project was formulated with an emphasis on in situ field experiments with more realistic boundary conditions and longer time scales compared with former experiments. As part of the project programme, a modelling inter-comparison has been conducted, involving the modelling of two experiments describing cement hydration on one hand and cement-rock reaction on the other, with teams representing the NDA (UK), Posiva (Finland), and JAEA (Japan).This modelling exercise showed that the dominant reaction pathways in the two experiments are fairly well understood and are consistent between the different modelling teams, although significant differences existed amongst the precise parameterisation (e.g. reactive surface areas, dependences of rate upon pH, types of secondary minerals), and in some instances, processes (e.g. partition of alkali elements between solids and liquid during cement hydration; kinetic models of cement hydration). It was not conclusive if certain processes such as surface complexation (preferred by some modellers, but not by others) played a role in the cement-rock experiment or not. These processes appear to be more relevant at early times in the experiment and the evolution at longer timescales was not affected. The observed permeability profile with time could not be matched. The fact that no secondary minerals could be observed and that the precipitated mass calculated during the simulations is minor might suggest that the permeability reduction does not have a chemical origin, although a small amount of precipitates at pore throats could have a large impact on permeability.The modelling exercises showed that there is an interest in keeping the numerical models as simple as possible and trying to obtain a reasonable fit with a minimum of processes, minerals and parameters. However, up-scaling processes and model parameterisation to the timescales appropriate to repository safety assessment are of considerable concern. Future modelling exercises of this type should focus on a suitable natural or industrial analogue that might aid assessing mineral-fluid reactions at these longer timescales. 相似文献
15.
CHAMP计划是由德国的波茨坦地球科学研究中心 (GFZ)提出 ,而且 ,目前已经付诸实施的科学计划之一。其目的在于通过获取大量近地观测资料来精化地球重力场模型 ,同时开展地球电磁场及地球大气重要参数的确定等研究。详细而全面地介绍该计划的科学目标 ,并评述了它将在建立地球重力场模型、地球电场模型、地球磁场模型和监测地球大气等方面所起的作用。 相似文献
16.
Alik Ismail-Zadeh Igor Tsepelev Chistopher Talbot Alexander Korotkii 《Tectonophysics》2004,387(1-4):81-103
Numerical studies of ductile deformations induced by salt movements have, until now, been restricted to two-dimensional (2D) modelling of diapirism. This paper suggests a numerical approach to model the evolution of three-dimensional (3D) salt structures toward increasing maturity. This approach is also used here to restore the evolution of salt structures through successive earlier stages. The numerical methodology is applied to study several model examples. We analyse a model of salt diapirs that develop from an initial random perturbation of the interface between salt and its overburden and restore the evolved salt diapirs to their initial stages. We show that the average restoration errors are less than 1%. An evolutionary model of a 2D salt wall loaded by a 2D pile of sediments predicts a decomposition of the salt wall into 3D diapiric structures when the overburden of salt is supplied by 3D synkinematic wedge of sediments. We model salt extrusion feeding a gravity current over the depositional surface and estimate an average rate of extrusion and horizontal velocity of salt spreading. Faulting of the overburden to salt overhangs initiates new secondary diapirs, and we analyse the growth of these secondary diapirs. We also study how lateral flow effects the evolution of salt diapirs. The shape of a salt diapir can be very different if the rate of horizontal flow is much greater than the initial rate of diapiric growth solely due to gravity. We discuss the applicability of the results of the models to the evolution of Late Permian salt structures in the Pricaspian basin (Russia and Kazakhstan). These structures are distinguishable into a variety of styles representing different stages of growth: salt pillows, diapirs, giant salt massifs, 2D diapiric walls and 3D stocks complicated by large overhangs. The different sizes, shapes and maturities of salt structures in different parts of the Pricaspian basin reflect areal differences in salt thickness and loading history. Our results suggest that the numerical methodology can be employed to analyse the evolution of all salt structures that have upbuilt through younger ductile overburdens. 相似文献
17.
S. Follin M.B. Stephens M. Laaksoharju A.-C. Nilsson J.A.T. Smellie E.-L. Tullborg 《Applied Geochemistry》2008
Three-dimensional, large-scale models for groundwater flow and solute transport are used for the low-temperature, fractured crystalline rock sites in Sweden that are being considered for the geological disposal of spent nuclear fuel. It has been suggested that comparisons between measured and simulated present-day hydrochemical data provide a means to constrain the complex influences of past climatic events and to improve the ability to understand the palaeohydrogeological evolution of the physical system studied. Here the authors demonstrate how the integration of multidisciplinary data and models from one of the sites in Sweden (Forsmark) can aid the appraisal of the hydrochemical conditions at 8000 BC, which is the selected starting point for the palaeohydrogeological modelling of the hydrochemical conditions in the Fennoscandian Shield during the Holocene (last 10 ka). Since a firm understanding of the evolution of the hydrochemical conditions is important for the long-term safety assessment, recognition of the initial hydrochemical conditions is essential for the overall build-up of confidence in the modelling process. 相似文献
18.
The boundary faults of faulted basins generally have segmental growth characteristics. Quantitative analysis of fault growth processes and combined models is of great significance for basin formation and evolution and hydrocarbon accumulation. Taking the Fulongquan fault depression in the southern part of the Songliao Basin as an example, using the 3D seismic data and using the fault-displacement length analysis method, the segmental growth and evolution process of the boundary fault is systematically studied, and the control effect of the spatial and temporal differential evolution of boundary faults on faulted basins is analyzed. The study shows that the segmental growth control of the boundary fault of Fulongquan fault depression forms a series of semi-mantle shoals; the sedimentary center of the Shahezi-Yingcheng fault is controlled to migrate from south to north; The slanting and thrusting activities control the height of the anticline trap; the transformation of the boundary fault property controls the evolution of the basin's tectonic pattern from the tandem semi-mantle to the faulted anticline. 相似文献
19.
The stratigraphic record and processes of turbidity current transformation across deep‐marine lobes 
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下载免费PDF全文 Ian A. Kane Anna S. M. Pontén Brita Vangdal Joris T. Eggenhuisen David M. Hodgson Yvonne T. Spychala 《Sedimentology》2017,64(5):1236-1273
Sedimentary facies in the distal parts of deep‐marine lobes can diverge significantly from those predicted by classical turbidite models, and sedimentological processes in these environments are poorly understood. This gap may be bridged using outcrop studies and theoretical models. In the Skoorsteenberg Formation (South Africa), a downstream transition from thickly bedded turbidite sandstones to argillaceous, internally layered hybrid beds, is observed. The hybrid beds have a characteristic stratigraphic and spatial distribution, being associated with bed successions which generally coarsen and thicken‐upward reflecting deposition on the fringes of lobes in a dominantly progradational system. Using a detailed characterization of bed types, including grain size, grain‐fabric and mineralogical analyses, a process‐model for flow evolution is developed. This is explored using a numerical suspension capacity model for radially spreading and decelerating turbidity currents. The new model shows how decelerating sediment suspensions can reach a critical suspension capacity threshold beyond which grains are not supported by fluid turbulence. Sand and silt particles, settling together with flocculated clay, may form low yield strength cohesive flows; development of these higher concentration lower boundary layer flows inhibits transfer of turbulent kinetic energy into the upper parts of the flow ultimately resulting in catastrophic loss of turbulence and collapse of the upper part of the flow. Advection distances of the now transitional to laminar flow are relatively long (several kilometres) suggesting relatively slow dewatering (several hours) of the low yield strength flows. The catastrophic loss of turbulence accounts for the presence of such beds in other fine‐grained systems without invoking external controls or large‐scale flow partitioning and also explains the abrupt pinch‐out of all divisions of these sandstones. Estimation of the point of flow transformation is a useful tool in the prediction of heterogeneity distribution in subsurface systems. 相似文献